In distributed communication or data processing systems, great demands are placed on the time synchronism of their components. The clock generators in these components are frequently synchronized to one another by interchanging data packets provided with timestamps via an asynchronous network or to a reference timer which can be reached via the asynchronous network.
The protocol currently used for clock and phase synchronization of clock generators via asynchronous networks is what is known as the PTP protocol (PTP: Precision Time Protocol), which is defined in the IEEE-1588 standard (IEEE: “Institute of Electrical and Electronic Engineers”). In this context, PTP messages are interchanged via the asynchronous network, for example using data packets which comply with the Internet Protocol.
PTP messages have to date been used primarily in networks and network segments which are small in size both geographically and logically. However, new techniques, particularly in the case of active network elements (switches, routers etc.), make it possible to use PTP messages in larger networks with a large number of “subscribers”, that is to say network elements, too. A drawback found in this context, however, is that PTP messages can be “monitored”. For example, known tools are what are known as “sniffers” which can be used to spy out all the data traffic in a network or network segment. Abusive analysis carried out in this regard on the registered (monitored) PTP messages can be used to infer the function and mode of operation of other network elements, which can be a problem for data integrity. It is also possible to “corrupt” PTP messages and hence disrupt the operation of other network elements. Finally, “genuine” PTP messages can also be recorded and repeatedly introduced into the network or network segment abusively, which likewise disrupts the operation of other network elements. The latter abusive processes are also known as “Denial-of-Service attacks”).